The movie “Deep Impact” hired multiple astronomers to serve as consultants in order to ensure accuracy when it came to the science behind the comet featured in the film. The team of advisors included Gene Shoemaker, one of the co-discoverers of the Shoemaker-Levy 9 comet, astronaut David Walker, Chris Luchini, and Joshua Colwell, a physics professor at the University of Central Florida. Colwell mentioned that the filmmakers made a conscious decision to make the movie as scientifically accurate as possible while still staying true to the story they wanted to tell.
The movie depicted both an attempt to deflect the comet and the creation of a subterranean “ark” to save a large number of people from the catastrophic effects of the impact. Colwell stated that both of these scenarios were plausible but would require extensive resources and time to execute. The advisors also ensured that the surface of the comet looked realistic and that its size in the movie was scientifically accurate, at seven miles across. They wanted the comet strike to resemble how an actual comet impact would occur and explored the consequences for Earth’s oceans, such as a massive tidal wave.
In terms of science, any celestial body with gravity would naturally be spherical due to isostatic adjustment. The smallest spherical body with its own gravity in the solar system is Mimas, which is approximately 246 miles in diameter. In contrast, the largest known comet, C/2014 UN271, has a diameter of only about 1.2 miles. The advisors for “Deep Impact” also made sure to show that astronauts visiting a comet would experience weightlessness near its surface, as expected in such an environment.